1. Field of the Invention
The present invention relates to a multiple welding gun system capable of welding a workpiece simultaneously at a plurality portions to be welded by using multiple (a plurality of) welding guns mounted on a robot arm of a single welding robot as a movable mount member.
2. Related Art
In a conventional automotive welding facility, a workpiece is welded spot by spot using a single welding gun mounted on a robot arm of a single welding robot as a mount member to which the welding guns are mounted.
Furthermore, in order to reduce tact time and equipment cost, a multiple welding gun system (two-head welding gun) has been provided performing spot-welding to a workpiece simultaneously at two-point (two-spot) welding portions by using two welding guns mounted on a robot arm of a single welding robot such as disclosed in Patent Document 1 (Japanese Utility Model Laid-Open Publication No. HEI 5-88773).
Furthermore, there is also known a multiple welding gun system (for example, including at least two welding guns) equipped with a pitch changing (space adjusting) device, in which one of welding guns is moved (slid) in parallel with the other one to thereby change a welding pitch (gun-to-gun spacing) of the welding guns.
However, the pitch changing device moving the welding guns in parallel has a complex in structure, and moreover, in order to set a large variable range of the welding pitch, it is necessary to increase parallel movement distance of the welding gun, resulting in increases in size and weight of the welding system accordingly.
Furthermore, with the pitch changing device, in a case where the parallel movement distance of the welding gun is increased, a moment acting on the multiple welding gun system is increased as well, which makes it necessary to increase rigidity of the multiple welding gun system including the pitch changing device. In this viewpoint, it is inevitable to increase the size and weight of the multiple welding gun system.